Method of printing and developing solvent images



METHOD OF PRINTING AND DEVELOPING SOLVENT IMAGES Filed Aug. 27, 1943 C. F. CARLSON May 8, 1951 2 Sheets-Sheet 1 INVENTOR.

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HIGH VOLT/Q65 y 1951 c. F. CARLSON 2,551,582

METHOD OF PRINTING AND DEVELOPING SOLVENT IMAGES Filed Aug. 27, 1943 2 Sheets-Sheet 2 Patented May 8, 1951 METHOD OF PRINTING AND DEVELOPING SOLVENT IMAGES Chester F. Carlson, Jackson Heights, N. Y.

Application August 27, 1943, Serial No. 500,207

11 Claims.

This invention relates to electrophotography.

An object of the invention is to improve the electrophoto process and the apparatus used therein.

Other objects will appear from the following description and the claims.

In the drawings:

Figure 1 illustrates an electrophoto camera device;

Figure 2 is a circuit diagram therefor;

Figure 3 illustrates a machine for copying transparencies and semi-transparencies; and

Figures 4 and 5 show modified means for charging the plate.

Electrophotography is described in my Patent 2,297,691 issued October 6, 1942. The process in its preferred form uses a plate carrying a coating of photoconductive insulating material on its surface. The coating is usually given a uniform electrostatic charge over its surface and the plate is then exposed in a camera or by other means to the picture to be copied.

The light falling on the coating discharges the electrostatic charge in proportion to the quantity of light reaching each part of the plate so that an electrostatic latent image is left on the plate. The highest charge will be retained on the areas receiving the least light and vice versa. The image is then developed by depositing a finely divided material on the plate. The material is attracted to the latent image in proportion to the strength of the residual charge. If the finely divided material is a dark colored powder the image is made visible immediately upon dusting the plate. The powder can be transferred and afiixed to a sheet of paper to produce the final copy.

In my co-pending application, Serial No. 365,- 888, filed November 16, 1940, now Patent 2,357,809, issued September 12, 1944, of which this is a continuation-in-part, an electro-photographic apparatus is shown for performing the above process automatically.

Another process of electrical photography is described in my Patent No. 2,221,776 issued November 19, 1940.

The present invention contemplates improvements in the above processes and apparatus including the use of a liquid mist, spray or fog for developing the image. Also contemplated are means for charging the plate and for the reversal of the charge on the plate during exposure. The use of an auxiliary electrode to control development is also a feature. Another feature resides in the methods of transferring the image to a sheet of paper or other material and producing a fixed visible copy thereon.

Another feature resides in an improved plate for use in the process. Other aspects and modifications of the invention will also be described.

Figure 1 illustrates an electrophoto camera for producing a complete finished print. The electrophoto plate is an endless belt 2|) of conductive material such as metal foil coated on the outer surface with a thin layer 2| of photoconductive insulating material, for example sulfur or anthracene. The belt is mounted to run on four insulating rollers 22, 23, 24, and 25. Roller 24 is arranged to be driven at relatively slow speed by a worm 26 driven by an electric motor to advance the belt clockwise around its circuit, under control of an electric switch.

A rotary brush 2'! is mounted adjacent roller 22 to brush against the surface of coating 2| to apply an electrostatic charge to its surface. The brush is enclosed in a metal shield 28, which makes contact with the surface of the brush.

A camera 29 comprising the usual lens 30, shutter 31, and focussing arrangements is mounted below the under face of the belt to focus the picture to be copied on the coatin 2|.

A mist developing chamber 32 is mounted adjacent the face of the belt where the belt passes from roller 23 to 24. It comprises a liquid reservoir 33 at its bottom and a row of atomizers 34 at spaced intervals along the edge of the reservoir. The atomizers 34 are fed with a liquid from reservoir 33 and air from a pressure pump 35 through tube 36 and header 31. Immediately above this reservoir is a bafile chamber 38 provided with a series of staggered bafiies 39 for removing large droplets from the mist produced by the atomizers. The top of the bafile chamber communicates by a slot, the walls of which serve as feed guides with a vertical passage 40 bounded by the coated side of belt 20 and by a plane metal electrode 41. The upper end of passage 40 com municates with a receiving slot 42 from which the air is led back to the pump by tube 43. Pump 35 may be a rotary positive compression pump, a reciprocating piston pump or other type adapted to deliver air under sufficient pressure to the atomizers.

A paper feed plate 44 is mounted above developing chamber 32 and a rubber pressure roller 45 is mounted to roll against the belt 20 where it passes over the roller 24. A suitable paper feed mechanism, such as a pusher 46, is provided to introduce the leading edge of a sheet of paper 31' under roller 45 at the appropriate moment.

A paper removal guide plate 48 is supported at the right of roller 24 to remove the sheet l! as it emerges from under roller 45. A coated roller 49 is mounted to receive the paper from plate 48. Roller 49 has a coating 50 of soluble dye which may be integral with the roller or may comprise a separate sheet similar to carbon paper, wrapped around the roller. For example: aniline blue, methyl violet, crystal violet, nigrosene or other dye may be dissolved in alcohol or higher boiling solvents and a sheet of paper may be saturated in the solution and allowed to dry after which it is wrapped around roller 49. Or a binder such as Vinsol resin, zein, ethyl cellulose, other resins and waxes or the like may be added and the solution applied to a sheet of paper as a coating or directly to the roller and allowed to dry. Insoluble pigments may also be added. A series of pressure rollers 51 are mounted adjacent roller 45 to apply pressure to the paper as it passes over the roller. Finally completed copy tray 52 is provided to receive the sheet as it leaves roller 49.

Roller 25 is covered with a cloth or felt layer I25 which engages the coated side of belt 20. A pair of partitions 53 and 3 form a partly enclosed passage I5 5 through which heated air can be circulated by a blower for drying the excess solvent from .belt 20, roller 49 and the finished prints which are deposited in tray 52. A hot plate 55 is mounted adjacent the belt for further drying effect.

A pair of infra-red lamps 56 are mounted inside the camera for infra-red flooding of the plate when required. A fine wire grid electrode 51 is is supported inside the camera a sufficient distance in front of belt 20 so that no distinct shadows are produced on the plate by light passing through the lens. A flood lamp 58 is also mounted within the camera to discharge the layer 2| When desired. Baffie channels 59 and 60 are provided at the edges of the camera where the belt 20 enters and leaves, to collect particles of dust or liquid and prevent their entry into the camera.

Figure 2 shows the electrical circuits for the machine. Motor 6| for driving worm 26 and motor 62 for rotating brush 2'! and hot air blower 63 for sending drying air through chamber I5 1 are all connected to the house current supply under control of switch 64. Air pump is separately driven from the electric supply under control of switch 65.

A high voltage generator 66, such as a transformer-rectifier system capable of supplying a small current at a potential of 1000 to several thousand volts is connected to the electric supply through switch 61, and feeds a high resistance voltage divider 68 connected across its output terminals. The mid-point of the resistance is grounded, shield 28 and grid 51 are connected to the negative terminal of the high voltage supply. Metal belt 20 can be connected to a tap B9, hormally near the positive end of resistance 68, by contact spring 10 and switch H. A terminal 12 is in contact with the liquid in reservoir 33 and isconnected to a tap 13 normally on the positive side of the center tap of the resistance 68. A terminal Ul is mounted in each atomizer opposite the aperture of the liquid jet and is connected to tap 15 on the negative side of the center tap. Electrode 4! is connected by conductor 78 to tap 11 which will normally bet set to a positive potential.

Operation.In the operation of the camerathe belt 20 is first rotated in a clockwise direction by motor 6| while brush 2'! is rotated to frictionally apply a uniform charge to the surface of photoconductive insulating layer 2!. If the layer is sulfur or anthracene the charge will normally be negative as these materials are near the negative end of the triboelectric series and acquire a negative charge when brought into contact with most materials such as the bristles oi the brush. During charging the high voltage generator may be operated to negatively charge shield 28 which thus acts to remove the positive charge received by the brush from layer 2!,

When a charged section of the belt has been advanced into the camera the motor El is stopped.

The lens 3%! of the camera is focussed on the subject, for example a sheet of drawings or documentary material spread on a table below the camera, or a three dimensional object to be photographed. The shutter 3! is opened for the desired exposure period and then closed. The optical image which is focussed 'on layer 2| renders the layer conductive in proportion to the qantity of light falling on it, so that during the exposure the electrostatic charge will be discharged from the illuminated areas in proportion to the quantity of light they receive. The remaining charge on the layer 2! will then comprise an electrostatic latent image corresponding to the optical image.

Fine wire grid 5i which is charged to a negative voltage accelerates the discharge of the layer by increasing the intensity of the electric field tending to move electrons in the layer toward plate 20. In fact, if exposure is continued long enough a reversal of charge will be produced on the most highly illuminated areas so that they will acquire a positive charge while the darker areas will retain their negative charge. In some cases it is desirable to accentuate the charge reversal still further and for this purpose switch TI is closed to apply a positive volta e to belt 20.

Some photoconductive materials exhibit a higher photoconductivity when radiated with infra-red radiation simultaneously with exposure to the photoelectrically active wave lengths and for this purpose a pair of infra red lamps 56 are mounted within the camera to flood the laye 22 with infra-red rays during exposure. This radiation is not itself photoelectrically active but merely increases the photoelectric efiect of the optical image entering through the camera lens.

Exposure having been completed motor 5! is started to advance the electrostatic image area past the mist developing chamber 32. At the same time air pump 35 is started to supply a current of liquid mist 78. The liquid in reservoir 33 which creates the mist is a solvent or solvent mixture. A slowly volatile solvent such as one boiling at l00-150 0., is preferred, for example amyl acetate, amyl alcohol, butyl alcohol, Cellosolve, toluene or mixtures, although less volatile materials such as cyclohexanol acetate and more volatile materials such as ethyl alcohol, ethyl acetate, alcohol-water mixtures and mixtures of high and low boiling solvents may be used in some cases.

As the liquid jet in each atomizer emerges from the fine liquid tube 80 into each atomizer air jet positive charges are induced on each droplet by the negatively charged electrode 14. The quantity of this charge on each droplet can be controlled by adjusting taps l3 and on voltage divider res stance.

The charged mist 18pm duced by atomizers 34 passes up around baflles 33 while the larger droplets are precipitated. A fine mist emerges at the top of the baflle chamber where it passes into the space 40 between belt 20 and electrode 4I. The positively charged mist droplets are strongly attracted to the negatively charged parts of the electrostatic latent image and deposit on layer 2| in a configuration corresponding to the image, and substantially inv proportion to the degree or charge.

At the top of space 40 the mist enters slot 42 and returns via header I8 and tube 43 to pump 35. Electrode M is movable to vary the space 40 between the electrode and plate 20 to adjust the linear velocity of the upwardly moving stream of mist. This" velocity should be low enough to permit capture of a. substantial number of mist droplets by the electrically charged areas of the image on the coating 2 I.

By adjusting the position of tap H on the voltage divider the positive (+l potential of electrode 4| can be regulated to produce an electric field between the electrode and plate 20 to drive a greater or lesser number of droplets toward the layer 2I It is thus possible to control the intensity and contrast of the developed image.

If exposure has been sufliciently long to give a charge reversal in the brightly illuminated areas so that these are positively charged the positive areas of the image will repel the droplets and permit the contrast to be further improved. Switch II may also be left closed during development if desired to repel the particles from the belt except where negative charges remain on the layer.

When the leading edge of the image area approaches roller 45 a sheet of paper 41 is advanced under roller 45 and as the liquid image is rolled against the paper most of the liquid is absorbed by the surface of the paper.

The paper is moved to the right and as it leaves the roller it is fed by plate 48 against the surface of roller 49 which has a surface layer 50 of dye which is soluble in the solvent liquid. Rollers 5| roll the paper firmly against surface 50. The liquid distributed on the paper in the configuration of the photographic image dissolves a small quantity of the dye as it passes over roller 49 to produce a visible dye image on the paper. The finished print is deposited in tray 52 ready for use. The solvent is slowly volatile so as to be retained on the paper until this stage. However, it soon dries leavingthe permanent dye image on the sheet. Since the paper absorbs most of the liquid very little is left on layers 2I or 50. Such solvent as remains is volatilized in the air stream flowing through passage I54. The coated belt 20 is thus returned to the camera ready for reuse.

Figure 3 shows a machine suitable for copying transparent or semi-transparent documents or drawings. It also embodies a modified develop-- ment process.

The construction of the machine be described in connection with its operation, which is as follows:

A strip of conductive sheet materialsuch as foil IOI having a coating I02 of photoconductive insulating material is unwound from a roll I00 and passed around a roller I03, then around a glass cylinder I04, then over rollers I05 and I06 and finally is Wound up in a roll [01.

A rotating brush I08 is mounted adjacentroller I03 to apply a frictional electric charge to coating I02 as the strip passes over roller I03.

Glass cylinder I04 contains lamps mounted in its interior such as incandescent lamps I09 and a tubular fluorescent lamp H0 which give a desirable combination of photo-electrically active wave lengths with infra-red radiation. A pair of adjustable shields III and H2 inside the cylinder serve to limit the area of exposure as desired.

A paper feed plate H3 is positioned adjacent the bottom of cylinder I04 where strip IOI begins to wind around it, so that a tracing or other transparent original H4 may be fed between the strip IOI and cylinder I04.

Cylinder I04 is driven at the desired speed by motor H5 through gear train H6 and as the charged strip IOI passes around it the original I I4 to be copied is fed between the strip and cylinder to expose the layer I02 to the image on the original. As original H4 emerges at the top of cylinder I04 it may be manually removed or rerouted around the cylinder to produce another copy as desired.

After exposure strip IOI passes around roller I05 and then upward to roller I06 along the face of a mist developing chamber I32 (similar to chamber 32 previously described). However, in this instance, instead of using a pure solvent or solvent mixture an ink or dye solution is used so that the image produced on coating I02 by the electrostatic precipitation of the mist becomes immediately visible. In some cases an ink containing suspended pigment may also be used in place of or supplementary to the dye solution. A dissolved binder can also be added.

A paper feed plate II'! is mounted adjacent the upper edge of roller I06 and a soft pressure roller H8 is mounted to roll a sheet of paper fed from plate II'I against the coating I02 as it emerges from developing chamber I 32. A pusher I I9 is provided to advance a sheet of plain paper I20 under roller H8 at the required instant. The dye solution applied by chamber I32 will then be transferred to the paper sheet I20 to produce a finished positive copy of the original I I4.

The finished print is received in tray I2I and the used portion of strip IOI is wound upon .rol'l I0! which is driven .by belt I22 and. slip-pulley I23 from a. pulley I24 mounted at one end of cylinder I04.

A certain amount of the dye image will remain on coating [02 after use. When the entire length of strip IOI has been run through the machine and collected on roll I01 the roll is removed from the machine and the coating washed or sponged with a dye solvent after which the strip is ready for reuse. In some instance, especially if sheets I20 are moistened, with solvent prior to use, it.

may be possible to reuse the strip IOI several times before. washing.

It is obvious that the development processes of either Figures 1 and 3 may be used interchangeably with both camera and transparency printing processes.

While any paper can be used for sheets 41 and I20, the best results are obtained with paper having a smooth absorbent surface. The paper used for spirit duplicators is very satisfactory. Where the absorbency of the paper is too high or too low for the best results it can be adjusted by applying thin coating of semi-absorbent material such as a mineral filler and a binder, or a material which is itself partly soluble in the solvent, such as zein, ethyl cellulose and combinations of these with other materials.

assnssa be of metal foil such as plain or etched aluminum or it'may be of paper, regenerated cellulose or a I particles are allowed to settle and the clear solution is applied to the conductive backing sheet by passing the sheet through a tank of the solution or painting with a fine brush or by spraying. It dries rapidly forming a thin, smooth adherent layer.

While one type of mist generator is shown and described it is contemplated that other atomizers, nebulizers, mist and fog generators can be used to generate the fine mist for development, For example, where an insulating liquid is used the liquid may acquire a charge by friction (contact potential) when issuing from the nozzle. Other suitable atomizers are shown and described in Freeman Patent 2,302,021; Campbell Patent 2,302,185 and Bramston-Cook Patent 2,302,289. It is also contemplated that in some cases an uncharged mist may be used.

Figure 4 shows an alternative method of charging the surface of coating 2! prior to exposure. This comprises a filament grid 200 of platinum or other filaments having electron emission coatings. The filaments are heated to emission temperature and connected to the negative terminal of the high voltage source while plate 20 is connected to the positive terminal of the source by spring contact ill. The electrons emitted from the filaments are attracted to the surface of the coating where they build up a uniform surface charge.

Figure 5 shows a further charging method. In this arrangement an electrode grid 20 I and a metal shield 252 are mounted in spaced relation to the coated surface 2! and a light source 283, such as a mercury or fluorescent lamp, is mounted behind the grid to illuminate the coating through the spaces in the grid. The grid 26% and meta].

shield 202 are connected to on terminal of the high voltage source and the plate 213 to the other terminal. The illumination from lamp 203 renders the coating 2i conductive to permit the electrodes to induce a charge on th layer. The charge is trapped on the layer when it passes under the shadow of shield 202 and into the camera. With this arrangement the coating may be given a positive charge if plate 29 is connected to the positive terminal of the source, as shown, or anegative charge if the connections are reversed.

By applying a negative or positive charge to the mist 18 produced by the atomizers it is possible to produce a negative or a positive reproduction. In one case the negative mist will deposit on the positively charged parts of the image and in the other case the positive mist deposits on the negative parts.

The walls of developing chamber 32 are of which will repel further charged particles and tend to keep them in suspension in the air stream.

It is obvious that the liquid development methods described herein are also applicable to the development of electrostatic latent images produced on insulating layers by other methods, such as those described in my Patent No. 2,221,776.

While the invention has been described as carried out in specific embodiments it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. The process which comprises producing an electrostatic latent image on a layer of insulating material, electrostatically depositing a fine liquid mist consisting of volatile material on said image to produce a liquid image, transferring the liquid image to a copy surface by pressing said surface against the liquid image and then bringing said copy surface into contact with a coloring material to pick up said coloring material on said liquid image.

2. The process which comprises producing an electrostatic latent image on a layer of insulating material, electrostatically depositing a fine solvent liquid mist consisting of volatile material on said image to produce a liquid image, transferring the liquid image to a copy sheet by pressing said sheet against the liquid image and then pressing the surface of said copy sheet against a dye-containing surface to pick up solubl dye in saidsolvent image.

3. The process which comprises producing an electrostatic latent image on a layer of insulating material, electrostatically depositing a fine solvent liquid mist consisting of volatile material on said image to produce a liquid image, transferring the liquid image to a copy sheet by rolling said insulating material with the exception of eleci sheet against the liquid image and then rolling said copy sheet against a surface carrying a solu' ble dye to pick up dye in said solvent image.

4. The process which comprises printing a solvent image consisting of volatile material on a paper surface, then pressing the surface against I a second surface charged with coloring material to produce an imageof said coloring material on said paper.

5. The process which comprises forming a solvent image on a substantially uniform surface, transferring said solvent image to a second surface by pressure contact, and evaporating any remaining solvent on the first-mentioned surface to prepare it to receive a new solvent image.

6. The process which comprises forming a solvent image consisting of volatile material on a substantially uniform surface, transferring said solvent image to a second surface by bringin said surfaces into pressure contact, and then bringing said second surface into pressure contact with a third surface charged with a soluble coloring ma terial to produce an image of said coloring material on said second surface.

7. The process which comprises forming a solvent image consisting of volatile material on a a to prepare it to receive a new solvent image, and

bringing said second surface into contact with a dry soluble coloring material to produce an image from said coloring material on said second surface.

8. The process which comprises producing an electrostatic latent image on a layer of insulating material, electrostatically depositing a fine solvent liquid mist consisting of volatile material on said image to produce a liquid image, transferring the liquid image to a copy surface, and then bringing the copy surface into contact with a dye soluble in said solvent liquid to produce a dye image.

9. The process which comprises producing an electrostatic latent image on a layer of insulating material, electrostatically depositing a solvent liquid mist consisting of volatile liquid on said image to produce a liquid image, transferrin the liquid image to a copy surface and evaporating any remaining solvent from said insulating layer to prepare said layer to receive a new image, bringing said copy surface into contact with a dye soluble in said solvent liquid to produce a dye image and evaporating said solvent from said dye image.

10. The method of developing an electrostatic latent image on a surface which comprises electrostatically depositing thereon a completely volatile liquid to produce a liquid image, transferring said liquid image to a copy surface and 10 tile material on said layer by electrostatic attraction to said latent image to produce a liquid image, transferring said liquid image to a copy surface, and evaporating any remaining solvent on said layer to prepare said plate to receive a new latent image.

CHESTER F. CARLSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 573,206 Chavez et a1 Dec. 15, 1896 999,949 Bell Aug, 8, 1911 1,565,256 Christensen Dec. 15, 1925 1,631,524 Dufay June 7, 1927 1,784,912 Scott Dec. 16, 1930 1,818,760 Selenyi Aug. 11, 1931 1,958,406 Darrah May 15, 1934 1,966,322 Tuttle July 10, 1934 1,966,907 Schneider July 17, 1934 1,989,717 Szegvari Feb. 5, 1935 2,221,467 Bleakney Nov. 12, 1940 2,221,776 Carlson Nov. 19, 1940 2,224,391 Huebner Dec. 10, 1940 2,251,190 Israel July 29, 1941 2,281,638 Sukumlyn May 5, 1942 2,297,691 Carlson Oct. 6, 1942 2,302,185 Campbell, Jr Nov. 17, 1942 2,357,809 Carlson Sept. 12, 1944 

